This invention generally relates to data storage devices for use with computers, and more particularly to hard disk drives.
Hard disk drives, also known as Winchester disk drives, are widely used within computer and electronic devices to store data. The relatively recent growth in demand for portable computers and removable hard disk devices has created a greater demand for damage tolerant drives that are resistant to mechanical shock. Furthermore, the introduction of sleep mode operation of hard disk drives to conserve energy has increased the number of start/stop cycles the drive must withstand, creating an additional need for increased durability.
A typical hard disk drive is composed of three major components: the electronics, the mechanics, and the media. The media portion of the drive generally comprises a disk which is coated with a material that is capable of recording data that is readable and writable by one or more heads. The material records the data in magnetic, optical, or magneto-optical modes, and the heads are appropriately designed to read and write the material coating the disk. The drive mechanics consist of the components necessary to rotate the media at a predetermined velocity and at a stable mechanical position. It also includes a suspension system for selectively positioning the heads at variable radial positions of the disk, as well as the components required for structural stability and an enclosed, clean operating environment. The drive electronics provide control, timing, data interpretation and transmission through an interface to other internal and external systems.
Information is stored in and retrieved from the media by means of read and write heads that write discretely polarized domains along tracks in the media to represent bits. These zones are detectable by the read head(s) moving over the tracks and sensing the changes in polarization of the domains. Among the many components within a disk drive, the interface between the read/write data heads and the storage media is the most sensitive to damage. Damage can occur during operation if a sudden impact causes the heads, which normally fly at a small distance above the surface of the rotating media, to crash or momentarily contact the rapidly spinning media. Any impact has the potential to cause a surface scratch or degradation that can diminish or destroy the usefulness of the media.
During non-operation a sudden impact can also cause damage to the media by causing the heads to move with respect to the media and damage the media either by the sliding action or impact due to momentary head-from-media separation (e.g., head slap). In addition, damage can occur during repeated start and stop operations in which the head must undergo a transition from media contact at zero media velocity to flying above the rotating media for read/write operation, and then re-land upon the media at the completion of use. For this reason, many schemes have been devised to minimize the potential for damage during head take off/landing and during head storage.
Typically, the read and write heads are suspended over the storage media by means of a flexible arm member commonly referred to as the head suspension assembly, or suspension. The suspension supports and positions the head, or slider, and applies a predetermined loading force which biases the slider toward impingement on the media. The slider is conformed to create lift when the media is rotating and a film of air is circulating with the disk, so that the slider is in stable flight spaced closely above the surface of the media. When the drive is first activated, the motor which rotates the disk must overcome the frictional forces created by the head dragging on the disk. The head must slide against the surface until sufficient air velocity is created under it to lift the head to its operational flying height. At this point, the slider lift counterbalances the suspension loading force. When the operation stops, the media is allowed to spin down, the air bearing collapses and the slider re-lands onto the media.
One approach in the prior art to overcoming the problems caused by the heads repeatedly taking off and landing on the media is to provide a ramp device, and drive the suspension to park on the ramp device whenever the media is rotating at less than air bearing velocity. Thus the slider is prevented from ever contacting the media. However, this arrangement does not prevent damage due to head slap while the disk system is operating. Indeed, portable and laptop computers often undergo movement during disk system operation, so the ramp device does not address a significant cause of media damage. Also, the ramp device is a generally stationary structure that does not engender the air bearing supporting the head assembly. Therefore, parking of the suspension on a ramp is unpredictable and disengagement of the suspension from the ramp clan create severe transient head flight instability and potential head crashing.